A Huge Step Forward in Quantum Computing Was Just Announced: The First-Ever Quantum Circuit

Australian researchers developed the first-ever quantum computer circuit, which has all the fundamental parts of a conventional computer chip but is scaled down to the quantum level.

"This is the most exciting discovery of my career," said senior author and quantum physicist Michelle Simmons, founder of Silicon Quantum Computing and director of the Center of Excellence for Quantum Computation and Communication Technology at UNSW.

Simmons and her colleagues not only developed what is basically a working quantum processor, but they also successfully tested it by simulating a tiny molecule with several quantum states, which is difficult for a conventional computer to do.

This implies that we are now one step closer to really using the capabilities of quantum computation to learn more about the world around us, even at the lowest scale.

"In the 1950s, Richard Feynman said we're never going to understand how the world works – how nature works – unless we can actually start to make it at the same scale," Simmons noted.

"If we can start to understand materials at that level, we can design things that have never been made before." 

How exactly can nature be controlled at that level is the question.

The most recent development comes after the group produced the first-ever quantum transistor in 2012.

(A transistor is a tiny electrical signal-controlling device that is only one component in a computer circuit. Since an integrated circuit combines several transistors, it is more complicated.

The researchers placed quantum dots with sub-nanometer accuracy in an ultra-high vacuum using a scanning tunneling microscope to accomplish this breakthrough in quantum computing.

To replicate how electrons hop along a string of single- and double-bonded carbons in a polyacetylene molecule, the circuit required precise positioning of each quantum dot.

Finding out exactly how many phosphorus atoms should be in each quantum dot, how far apart each dot should be, and then designing a machine that could arrange the small dots in precisely the appropriate layout inside the silicon chip were the difficult portions.

According to the researchers, if the quantum dots are too huge, their interaction becomes "too large to independently control them".

The amount of energy required to add another electron to the dot may be significantly altered by each additional phosphorus atom, therefore if the dots are too tiny, randomness is introduced.

The finished quantum chip had ten quantum dots on it, each of which was composed of a modest number of phosphorus atoms.

Less space between the quantum dots than between single carbon bonds was used to imitate double carbon bonds.

In order to demonstrate that the computer was accurately replicating the passage of electrons through the molecule, Polyacetylene was used since it is a well-known model.

Because big molecules are just too complicated for conventional computers to simulate, quantum computers are required.

For instance, a traditional computer would require 1086 transistors to simulate the penicillin molecule with 41 atoms, which is "more transistors than there are atoms in the observable universe"

It would only be necessary for a quantum computer to have a processor of 286 qubits (quantum bits).

The development of novel materials involves a lot of guesswork since scientists currently have limited visibility into how molecules behave at the atomic level.

"One of the holy grails has always been making a high temperature superconductor," according to Simmons. "People just don't know the mechanism for how it works." 

The study of artificial photosynthesis and how light is transformed to chemical energy through an organic chain of processes is another possible use for quantum computing.

The production of fertilizers is another significant issue that quantum computers might aid in resolving. Currently, in the presence of an iron catalyst, triple nitrogen bonds are broken under high pressure and temperature conditions to produce fixed nitrogen for fertilizer.

It would be very cost- and energy-efficient to find an alternative catalyst that can produce fertilizer more efficiently.

According to Simmons, the path used by the creators of conventional computers to go from quantum transistor to circuit in roughly nine years is being mimicked.

In 1947, the first transistor for a traditional computer was developed. In 1958, the first integrated circuit was created. There were 11 years between the two discoveries, and Simmons' team completed the transition two years early.

This article was published in Nature.